France's former ruling UMP party is refusing to join forces with the Socialists to block the far-right Front National from gaining seats in parliament.

The left, on track to win a majority of seats in the second-round vote on Sunday, had called for a "republican front" against the FN, which scored highly in about 60 constituencies.

UMP officials are due to meet on Monday afternoon to make a formal decision on how to deal with "triangulaires" – constituencies in which the Parti Socialiste, the FN, headed by Marine Le Pen, and the UMP are in the second round.

However, Jean-François Copé, head of the UMP, which was thrown out of government after Nicolas Sarkozy lost the presidential election to the Socialist's François Hollande in May, said his party was not interested in making deals. He said the party preferred to appeal to FN voters to support the mainstream right in the run-off vote to defeat the left.

Martine Aubry, the Parti Socialiste leader, reminded Copé that the party had called on its supporters to vote for the UMP's Jacques Chirac in 2002, when the then head of the FN, Jean-Marie Le Pen, won a surprise victory through to the second round, knocking out the PS candidate. "We are calling for a defeat of the FN," she told French radio.

The FN hopes to win its first parliamentary seats for nearly 26 years, but is expected to win fewer than three constituencies. Marine Le Pen succeeded in defeating the Front de Gauche candidate, Jean-Luc Mélenchon, in the industrial heartland of northern France. Her niece Marion Maréchal-Le Pen, 22, also won the first round in her Provence constituency. In past elections, however, FN expectations have been dashed by other parties uniting against them.

Six government ministers, including the prime minister, Jean-Marc Ayrault, obtained an absolute majority of votes in the first round. The PS is quietly confident other ministers will win their seats, removing the spectre of an emergency cabinet reshuffle: Hollande has warned that any minister who loses their seat will lose their government job.

The most high-profile socialist at risk is Ségolène Royal, a presidential election candidate in 2007 and former partner of Hollande, who is in a close two-way battle with a dissident PS member in her south-west constituency. She hopes to be named president of the Assemblée National.

The two-round parliamentary elections, which since 2002 have followed the presidential elections, are complicated and difficult to predict.

The French left confounded pollsters and analysts who predicted it would find it difficult to obtain a clear majority in the Assemblée Nationale, the lower house of parliament. The Parti Socialiste controls the upper house, the Sénat.